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MidpointRounding Enumeration

Specifies how mathematical rounding methods should process a number that is midway between two numbers.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

[ComVisibleAttribute(true)]
public enum class MidpointRounding

Member nameDescription
ToEvenWhen a number is halfway between two others, it is rounded toward the nearest even number.
AwayFromZeroWhen a number is halfway between two others, it is rounded toward the nearest number that is away from zero.

Use MidpointRounding with appropriate overloads of Math::Round to provide more control of the rounding process.

A rounding operation takes an original number with an implicit or specified precision; examines the next digit, which is at that precision plus one; and returns the nearest number with the same precision as the original number. For positive numbers, if the next digit is from 0 through 4, the nearest number is toward negative infinity. If the next digit is from 6 through 9, the nearest number is toward positive infinity. For negative numbers, if the next digit is from 0 through 4, the nearest number is toward positive infinity. If the next digit is from 6 through 9, the nearest number is toward negative infinity.

In the previous cases, the MidpointRounding enumeration does not affect the result of the rounding operation. However, if the next digit is 5, which is the midpoint between two possible results, the nearest number is ambiguous. In this case, the MidpointRounding enumeration enables you to specify whether the rounding operation returns the nearest number away from zero or the nearest even number.

The following table demonstrates the results of rounding some negative and positive numbers in conjunction with the values of MidpointRounding. The precision used to round the numbers is zero, which means the number after the decimal point affects the rounding operation. For example, for the number -2.5, the digit after the decimal point is 5. Because that digit is the midpoint, you can use a MidpointRounding value to determine the result of rounding. If AwayFromZero is specified, -3 is returned because it is the nearest number away from zero with a precision of zero. If ToEven is specified, -2 is returned because it is the nearest even number with a precision of zero.

Original number

AwayFromZero

ToEven

3.5

4

4

2.8

3

3

2.5

3

2

2.1

2

2

-2.1

-2

-2

-2.5

-3

-2

-2.8

-3

-3

-3.5

-4

-4

The following code example demonstrates the Round method in conjunction with the MidpointRounding enumeration.

// This example demonstrates the Math.Round() method in conjunction  
// with the MidpointRounding enumeration. 
using namespace System;

void main()
{
    Decimal result = (Decimal) 0.0;
    Decimal posValue = (Decimal) 3.45;
    Decimal negValue = (Decimal) -3.45;

    // By default, round a positive and a negative value to the nearest 
    // even number. The precision of the result is 1 decimal place.
    result = Math::Round(posValue, 1);
    Console::WriteLine("{0,4} = Math.Round({1,5}, 1)", result, posValue);
    result = Math::Round(negValue, 1);
    Console::WriteLine("{0,4} = Math.Round({1,5}, 1)", result, negValue);
    Console::WriteLine();

    // Round a positive value to the nearest even number, then to the 
    // nearest number away from zero. The precision of the result is 1 
    // decimal place.
    result = Math::Round(posValue, 1, MidpointRounding::ToEven);
    Console::WriteLine(
        "{0,4} = Math.Round({1,5}, 1, MidpointRounding.ToEven)",
        result, posValue);
    result = Math::Round(posValue, 1, MidpointRounding::AwayFromZero);
    Console::WriteLine(
        "{0,4} = Math.Round({1,5}, 1, MidpointRounding.AwayFromZero)",
        result, posValue);
    Console::WriteLine();

    // Round a negative value to the nearest even number, then to the 
    // nearest number away from zero. The precision of the result is 1 
    // decimal place.
    result = Math::Round(negValue, 1, MidpointRounding::ToEven);
    Console::WriteLine(
        "{0,4} = Math.Round({1,5}, 1, MidpointRounding.ToEven)",
        result, negValue);
    result = Math::Round(negValue, 1, MidpointRounding::AwayFromZero);
    Console::WriteLine(
        "{0,4} = Math.Round({1,5}, 1, MidpointRounding.AwayFromZero)",
        result, negValue);
    Console::WriteLine();
}

/*
This code example produces the following results:

3.4 = Math.Round( 3.45, 1)
-3.4 = Math.Round(-3.45, 1)

3.4 = Math.Round( 3.45, 1, MidpointRounding.ToEven)
3.5 = Math.Round( 3.45, 1, MidpointRounding.AwayFromZero)

-3.4 = Math.Round(-3.45, 1, MidpointRounding.ToEven)
-3.5 = Math.Round(-3.45, 1, MidpointRounding.AwayFromZero)

*/

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

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